Some like linear pots on volume for a more consistent taper. Volume doesn't jump so much between 10 to 8 and then shelving below. Way more gradual which some people prefer. I like 500ka with a 220k resistor across the input and output lugs for a more gradual taper which turns out to be something between a log and linear taper.Originally Posted by Simon Barden
Proper log pots should be smooth all the way down with no jumping between 8 and 10. On any pot there's normally a dead area between 10 and 9 where nothing happens and then the resestance starts to kick in, but you'd get that with a linear pot as well (just refer to the manufacturers resistance charts). But nothing is really done isolation in a guitar/amp combination and the perceived response can vary depending on how clean or driven the amp is - or how any pedals are set.
A linear pot shouldn't have a perceived consistent taper, as hearing is definitely logarithmic and to get a smooth reduction in heard output, you will need a log pot. Though there are different variations on a log slope as it depends what the starting value for the curve is. You can't start from zero so the design curve has to start from a small finite resistance value which can vary quite a bit, which is why you get so many possible pot curves available from people like CTS, with 5%, 10% and 20"% resistance (or your choice for custom orders) at the 50% position. That curve is normally then approximated with two linear responses, as very few log pots have true log responses (requiring laser-cut resistance tracks). So the audio response will vary depending on the selected log curve and how well the manufacturer can replicate it within the pot.
A linear one simply can't give anything like as smooth a volume response as a log one (based on physics/acoustics). But it may well do what a particular player wants in terms of speed of response to turning a knob, so it comes down to personal preference. A log taper should suit most people, but if linear does it for you, then that's fine.
Edit: Looking at the CTS curves again, for log curves, only the lower part of the curve is linear, the upper part is actually curved (though the curve isn't quite the curve you'd expect to see if it was a single curve and there is a bit of a compromise around the 50% position area).
Last edited by Simon Barden; 03-10-2020 at 12:57 AM.
There was a time that I played around a lot with pots, and found pretty much exactly what Simon is saying to be observable.
My sense is that with most of the pots that are common in guitars the "curve" is actually two or three straight lines with different slopes as in line "3"...
...I have heard this given as a reason that log pots are often not smooth, I am not sure how audible the difference is between an actual curve and an approximation of a curve.
As with everything audio, if you can it's generally best to test, and there is a lot to be said for trying different values. I now build all of my control stacks outside the guitar so that I can get a sense of how things sound before I have to "commit" and get everything wired in. It's why the tone cap on my recent Strat-style build is physically located in the under the jack plate. That way I could try several different ones with the pickups in place before committing. I am glad to have done this because the one I liked the best was different than what the mfg recommended. Same can go for pots. You may be happiest if you try both kinds of pots to see which you like best. It's an interesting experiment if nothing else.
I needed to draw this circuit out so I could understand it. Here it is in case it's useful for anyone else.
Posting Permissions
Reply With Quote